One to watch: Inspector George Gently - BBC One, 8.30pm

So while the 1960s might seem a straightforward enough setting for a police drama, it can only run so far before the laid-back era begins to shift towards the more cynical 1970s, heralding a shift in attitudes towards the police.

And that’s exactly where Inspector George Gently succeeds tonight, as it returns for a sixth series.

As the story progresses, we begin to realise that not only are our two heroes, Gently and Bacchus, forever changed by the explosive events of last season, but that the world they police is also adapting, and becoming - if you can imagine it - even more hostile.

It’s hardly surprising, then, that following the shooting in Durham Cathedral which almost cost both men their lives, Bacchus has lost his confidence.

Gently is shocked when the formerly ambitious sergeant hands in his resignation, but is determined to do his best to set his protégé back on track - although he doesn’t do so in a particularly compassionate manner.

However, convincing Bacchus he needs his help on one last case while he works out his notice, Gently takes him along to investigate a death in custody.

The victim was arrested after Newcastle Police’s efforts to clear out a slum resulted in riots, but after spending a night in the cells, was discovered dead the following morning.

During the course of their investigation, they learn that the police force is no longer viewed in terms of the helpful and familiar faces of ‘bobbies on the beat’, but are now perceived as being untrustworthy agents of the State.

Lee Ingleby, who plays Bacchus, explains “It’s the modernisation of the world and the North East catching up with the rest of the country. It’s upsetting communities saying they will modernise whether they like it or not - and it’s the same with the police.”

At a time when both Gently and Bacchus are dealing with the after-effects of last season’s shooting, this case presents a fresh set of challenges for them both. But will it be enough to tempt Bacchus back to the fray, or is he too far gone?

Where this programme, based on the Inspector Gently novels by Alan Hunter, truly succeeds is not simply in its plots - although the leads always have some intriguing cases to solve - but in the subtle characterisation.

Many police dramas think a cop’s only dilemma is ‘whodunit?’, but through the past five series we’ve seen an emphasis on the ‘whys’ - and not just in terms of the criminals, either, for here we get a glimpse into our heroes’ motivations.

It makes for compelling telly, as the more we know about the protagonists, the easier it is to get behind them.

We’re hoping for plenty more where this came from - although another series would bring us bang into the 1970s.

Judging by Bacchus’s sideburns, though, we’re halfway there already...